Spontaneous Orthogonal Self‐Assembly of a Synergetic Gelator System

Abstract

exhaustively developed over the past two decades, [1,2] however the recent interest for advanced functional nanomaterials has made this area of research particularly exciting.[3] Organogels based on low molecular weight organic gelators (LMWOGs) are formed by self-assembled fibrillar networks (SAFINs), which are produced by a combination of weak non-covalent physical interactions including hydrogen bonding, p-p stacking, dipole-dipole or donor-acceptor interactions, metal coordination and van der Waals interactions. Gels based on strong chemical bonds cannot be redissolved and consequently, they do not show thermoreversible gel-sol transitions. The enhancement of the mechanical strength and thermostabilities of the gels has therefore become crucial for numerous applications in the area of material science.In view of some of the applications of gelator systems, we recently became interested in organic non-covalent interpenetrating polymer network (IPN) [4] materials, more specifically, in the investigation of 3D organogel networks and their effects on the physico-chemical properties in the systems. Different groups have reported various examples of these innovative materials, which are synthesised under suitable conditions and characterised by a special network structure consisting of two types of morphologies of different physico-chemical nature. [5] Van Esch and co-workers have recently reported that hydrogelators could undergo an orthogonal, independent selfassembly process in the presence of micellar and vesicular aggregates, with the subsequent coexistence of gel fibres within the formed nanostructures. [6] Herein, we report the potential of two gelator systems (with different solvent-dependent abilities) to gel by self-assembly processes and their ability to spontaneously self-organise and simultaneously assemble into a novel nanomaterial containing two different interconnected porous and fibre-type domains. The final nanomaterial can remarkably improve the properties of related or similarly generated independent organogels. The multi-gelator gels [7] comprise two different types of aggregates, which are spontaneously and simultaneously assembled.With this purpose, we employed a mixture of two different organogelators 1 and 2. Firstly, organogelator 1 is a synergistic multi-component organogelator liquid system, in which the gelation phenomenon of oxygenated solvents takes place at low temperature (after gentle heating of the isotropic solution). Organogelator 2 is an oligoamide, which exclusively produces stable organogels in chlorinated solvents upon cooling of the gently heated isotropic solution. The organogel properties of both gelator systems (1 and 2) have been reported previously. [8,9] All the gels were tested in tetrahydrofuran/chloroform (9:1 ratio). Hunters oligoamide (2) is a well-known MWOG selectively for chlorinated solvents, at concentrations in the 0.4-3.8 wt % range.[9] However, it does not gel solvents such as THF, diethyl ether or acetonitrile (precipitation occurs upon cooling of the is...

Multicomponent low molecular weight gelators

“…There are a number of examples for both mixed and self-sorted systems where the rheological properties are improved compared to what might be expected from the individual components. 78,86,91,100,101 Even from these relatively few examples however, it is clear that there is not a simple link between the rheological data and the type of assembly.…”

The effect of self-sorting and co-assembly on the mechanical properties of low molecular weight hydrogels

“…10 Many LMWG are thermally triggered, assembling into fibres when a hot solution is cooled. 12,17,[20][21][22][23] For example, a mixed LMWG system was thermally gelled, with the final rheological properties being significantly higher than for either LMWG alone. 24 This mechanical reinforcement was explained as being due to co-assembly.…”

Chemically programmed self-sorting of gelator networks

“…Self-sorting in supramolecular gel phases is a rare phenomenon and, at present, always achieved via thermally induced gelation [6][7][8][9][10][11][12] . Typically, a solution containing the two types of gelator molecule is heated above the temperature required to dissolve both completely.…”

“…On cooling, one molecule assembles at a higher temperature than the other, which can result in a self-sorted network. Formation of such a self-sorted network is often inferred from visual differences between self-assembled structures as imaged by scanning electron microscopy (SEM), atomic force microscopy or transmission electron microscopy (TEM) [6][7][8] . For example, Shinkai and colleagues 5 have demonstrated that a bulk heterojunction can be formed via the thermal self-sorting of two specific gelators that selfassemble to form fibres, with the junctions between fibres giving rise to the heterojunction.…”